Effects of nitrogen deposition and biochar amendment on soil respiration in a Torreya grandis orchard

Abstract

Torreya grandis is an important economic nut tree species in southeastern China, but there is little information about its CO2 efflux under increasing atmospheric nitrogen (N) deposition. There are few studies that assess the response of soil respiration to biochar applications in orchard soils under N deposition conditions. We investigated changes in soil respiration rate and other environmental factors under a factorial combination of biochar amendment (BC0: 0 t ha−1, BC1: 20 t ha−1, BC2: 40 t ha−1) and simulated additional N deposition (N0: 0 kg N ha−1 yr−1, NL: 30 kg N ha−1 yr−1 and NH: 60 kg N ha−1 yr−1) treatments over three years (2016–2018). Soil respiration rate showed significant seasonal changes, with the highest rates occurring in summer and the lowest occurring in winter. The annual CO2 emission amount of the control was 3.1 ± 0.03 kg CO2 m−2. Nitrogen deposition significantly increased soil respiration, but the positive effects of high-N treatment decreased over time. Meanwhile, N deposition significantly decreased both the soil temperature sensitivity (Q10-soil) and air temperature sensitivity (Q10-air) of soil respiration. Biochar amendment significantly increased soil respiration in the first and third years. However, only BC2 reduced Q10-soil and Q10-air. The effects of biochar amendment on soil respiration varied with the level of N deposition. Three-factor analysis of variance showed that N deposition, biochar amendment, and time all had significant effects on soil respiration. Our results indicate that biochar could not effectively inhibit the promotion effect of N deposition on soil respiration in T. grandis orchard but may reduce soil carbon emission caused by future climate warming.